1. Field of the Invention
The present invention relates to a scroll type compressor, and more particularly, to a scroll type compressor having an injection mechanism through which a portion of the refrigerant flowing from the condenser is introduced into the intermediately compressed refrigerant in the compressor.
2. Description of the Prior Art
As known in this technical field, a refrigeration circuit includes a compressor, a condenser, an expansion device and an evaporator all connected in series.
In operation of the refrigeration circuit, the vaporized refrigerant conducted into the compressor from the evaporator is compressed, and is then discharged to the condenser. The refrigerant in the condenser is liquefied by radiating heat therefrom. The liquefied refrigerant in the condenser is then conducted to the expansion device, and is expanded due to the reduction in pressure as the liquefied refrigerant flows therethrough. The expanded refrigerant further flows into the evaporator, and is vaporized due to the absorption of heat. The vaporized refrigerant in the evaporator is returned to the compressor so that the above processes can then be repeated.
A modified refrigeration circuit in which a condenser is used for heating purposes is discussed in Issued Japanese Patent No. 64-10675. Referring to FIG. 1, the modified refrigeration circuit includes motor driven hermetic type scroll compressor 1, condenser 2, first expansion device 3, liquid-vapor separator 4 from which the liquefied refrigerant and the gaseous refrigerant flow out through first and second outlets 4a and 4b thereof, respectively, second expansion device 5 and evaporator 6. An outlet of compressor 1 is connected to an inlet of condenser 2, which in turn has an outlet connected to an inlet of first expansion device 3. An outlet of first expansion device 3 is connected to an inlet of separator 4 and a first outlet 4a of separator 4 is connected to an inlet of second expansion device 5. An outlet of second expansion device 5 is connected to an inlet of evaporator 6, the outlet of which is connected to an inlet of compressor 1, so as to complete the refrigeration circuit.
The modified refrigeration circuit further includes a pipe member 7 which fluidly connects second outlet 4b of liquid-vapor separator 4 with the intermediately located sealed-off fluid pockets of the scroll compressor. The pressure in the intermediately located sealed-off fluid pockets is lower than the pressure in second outlet 4b of separator 4. A valve element such as electromagnetic valve 8 is also provided at pipe member 7 so as to selectively communicate the intermediately located sealed-off fluid pockets with second outlet 4b of separator 4. In FIG. 1, arrow "A" indicates the refrigerant flow in the modified refrigeration circuit.
In operation of the modified refrigeration circuit, the gaseous refrigerant which flows from separator 4 through second outlet 4b is conducted into the intermediately located sealed-off fluid pockets of the scroll elements through pipe member 7 so as to be combined with the gaseous refrigerant which was taken into the outermost fluid pockets of the scroll elements from the evaporator and then continuously compressed. The combined gaseous refrigerant in the intermediately located sealed-off fluid pockets is further compressed, and is then discharged to condenser 2. Accordingly, the amount of gaseous refrigerant flowing into condenser 2 from compressor 1 is increased without increasing the capacity of compressor 1, and thus, the amount of heat radiation from the refrigerant in condenser 2 is likewise increased without increasing the capacity of compressor 1.
The above-described refrigeration method, that is, combining vaporized refrigerant flowing from the condenser and through the liquid-vapor separator with the intermediately compressed refrigerant in the compressor is generally called "gas injection". Therefore, the method is simply described as "gas injection" hereinafter for convenience.
The above-mentioned '675 Japanese patent discloses a motor driven hermetic type scroll compressor utilized in the modified refrigeration circuit shown in FIG. 1. Referring also to FIG. 2, motor driven hermetic type scroll compressor 100' includes hermetically sealed casing 110 which comprises cylindrical portion 111 and a pair of plate-shaped portions 112a and 112b which are hermetically connected to an upper end and a lower end of cylindrical portion 111, respectively, by brazing, for example.
Casing 110 houses fixed scroll 10, orbiting scroll 20, block member 30, driving mechanism 50 and a rotation-preventing mechanism, such as Oldham coupling 60. Fixed scroll 10 includes circular end plate 11 from which spiral element 12 extends. Orbiting scroll 20 includes circular end plate 21 from which spiral element 22 extends. Block member 30 is firmly secured to an upper inner peripheral wall of cylindrical portion 111.
Circular end plate 11 is attached by a plurality of fastening members, such as bolts (not shown), to block member 30 in order to define chamber 40 in which orbiting scroll 20 is disposed. Spiral elements 12 and 22 are interfitted at an angular and a radial offset to produce a plurality of linear contacts defining at least one pair of sealed-off fluid pockets. Driving mechanism 50, which includes rotatably supported drive shaft 51, is connected to orbiting scroll 20 to effect the orbital motion of orbiting scroll 20. Oldham coupling 60 is disposed between circular end plate 21 and block member 30 to prevent the rotation of orbiting scroll 20 during its orbital motion.
Circular end plate 21 of orbiting scroll 20 divides chamber 40 into first chamber 41 in which spiral elements 12 and 22 are disposed and second chamber 42 in which Oldham coupling 60 and crank pin 52 of driving mechanism 50 are disposed. Discharge port 70 is formed at a central portion of circular end plate 11 to discharge the compressed fluid from a central fluid pocket.
Drive shaft 51 is rotatably supported in a bore 31 that is centrally formed in block member 30. First and second plain bearings 52a and 52b are axially spaced from each other by a given distance and are disposed between an inner peripheral surface of bore 31 and an outer peripheral surface of drive shaft 51.
Casing 110 further houses motor 53 for rotating drive shaft 51. Motor 53 includes ring-shaped stator 53a and ring-shaped rotor 53b. Stator 53a is firmly secured to the inner peripheral wall of cylindrical portion 111 and rotor 53b is firmly secured to drive shaft 51. An axial hole (not shown) is formed in drive shaft 51 to supply lubricating oil 55 collected in the bottom of casing 110 to a gap between the outer peripheral surface of drive shaft 51 and an inner peripheral surface of bearings 52a and 52b.
In order to supply suction fluid to the outermost fluid pockets, one end of radial inlet port 83 is hermetically sealed to cylindrical portion 111 and is connected to suction port 80 formed in a peripheral portion of circular end plate 11. The other end of radial inlet port 83 is connected to the outlet of evaporator 6. One end of radial outlet port 73 is also hermetically sealed to cylindrical portion 111 in order to establish fluid communication with the inner space 101 of casing 110. The other end of radial outlet port 73 is connected to the inlet of condenser 2.
One end of pipe member 7 is connected to second outlet 4b of liquid-vapor separator 4. The other end of pipe member 7 is hermetically sealed to upper plate-shaped portion 112a and is connected to one end of pipe member 91. Pipe member 91 is disposed within inner space 101 of casing 110 above fixed scroll 10. Pipe member 91 is forked into portions 91a and 91b which are connected to a pair of axial holes 13 formed through circular end plate 11 of fixed scroll 10. Each axial hole 13 includes a large diameter portion 13a and a small diameter portion 13b extending downwardly from a lower end thereof. Holes 13 link portions 91a and 91b of pipe member 91 to a pair of intermediately located sealed-off fluid pockets 92, in which the pressure is lower than the pressure in second outlet 4b of separator 4. Pipe members 7 and 91 and axial holes 13 thereby form gas injection mechanism 90'.
In operation, suction gas entering suction port 80 from evaporator 6 flows through inlet port 83 into the outermost fluid pockets of the scroll elements, and is then compressed by virtue of the orbital motion of orbiting scroll 20. The gaseous refrigerant which flows from liquid-vapor separator 4 through second outlet 4b is introduced into the intermediately located sealed-off fluid pockets 92 of the scroll elements via pipe members 7 and 91 and axial holes 13 so as to be combined with the gaseous refrigerant which was taken into the outermost fluid pockets 92 of the scroll elements and continuously compressed. The combined gaseous refrigerant in intermediately located sealed-off fluid pockets 92 is further compressed, and is discharged from the centrally located sealed-off fluid pocket through discharge port 70. The discharged refrigerant gas thereby fills the entirety of inner space 101 of casing 100, except for chamber 40. The discharged refrigerant gas within inner space 101 of casing 100 flows to condenser 2 through outlet port 73.
In the above-described '675 Japanese patent, gas injection mechanism 90' includes a plurality of connecting portions, such as, the connecting portion between pipe member 91 and pipe member 7, and the connecting portions between holes 13 and forked portions 91a and 91b of pipe member 91. Therefore, when compressor 100' is assembled, a complicated process is required for assembling gas injection mechanism 90'. This causes an increase in the manufacturing cost of the compressor.
Another modified refrigeration circuit illustrated in FIG. 1a is discussed in Japanese Patent Application Publication No. 60-166778. The same numerals are used in FIG. 1a to denote the corresponding elements shown in FIG. 1, and an explanation thereof is omitted. In the embodiment of FIG. 1a, the modified refrigeration circuit includes pipe member 7 having one end connected for fluid communication with the refrigerant flowing between condenser 2 and expansion device 5, and further including an additional expansion device 9 provided along pipe member 7. The other end of pipe member 7 is connected to the scroll compressor intermediately located sealed-off fluid pockets in which the pressure is lower than the pressure in the portion of pipe member 7 located on the downstream side of additional expansion device 9.
In operation of this modified refrigeration circuit, a part of the liquefied refrigerant which flows from condenser 2 is diverged into pipe member 7, and flows through additional expansion device 9 thereby reducing the pressure thereof. The reduced pressure liquefied refrigerant is next introduced into the intermediately located sealed-off fluid pockets of the scroll elements through pipe member 7 to be combined with the gaseous refrigerant which was taken from the evaporator into the outermost fluid pockets of the scroll elements and was continuously compressed. At this stage, the scroll elements and the gaseous refrigerant in the intermediately located sealed-off fluid pockets of the scroll elements are cooled by vaporization of the reduced pressure liquefied refrigerant from condenser 2. The combined gaseous refrigerant at the intermediately located sealed-off fluid pockets is further continuously compressed, and is then discharged to condenser 2. Accordingly, the operation of the compressor at a thermally severe condition can be prevented and the overheating thereof can thus be avoided. The above-described refrigeration method, that is, introducing the reduced pressure liquefied refrigerant from the condenser through the additional expansion valve to the intermediately compressed refrigerant in the compressor is generally called "liquid injection". Therefore, for convenience, this method is simply referred to as "liquid injection" hereinafter. For further convenience, "gas injection" and "liquid injection" are generally described as "injection" hereinafter.
If motor driven hermetic type scroll compressor 100' of FIG. 2 is utilized in the modified refrigeration circuit of FIG. 1a, the thermal influence of the discharged high temperature refrigerant gas in inner space 101 of casing 100 on pipe member 91, which is exposed to the discharged refrigerant gas in inner space 101 of casing 100, is not negligible because the mass of pipe member 91 is small, and therefore, the thermal capacity of pipe member 91 is correspondingly small. Hence, a large part of the reduced pressure liquefied refrigerant from condenser 2 passing through additional expansion device 9 is vaporized in pipe member 91. Accordingly, the scroll elements and the gaseous refrigerant in intermediately located sealed-off fluid pockets 92 of the scroll elements may not be effectively cooled and compressor 100' may ultimately operate at a thermally severe condition.